1. Field of the Invention
The present invention relates to a cooling structure for an internal combustion engine, in which: a spacer is fitted inside a water jacket which is formed to surround peripheries of a plurality of cylinder bores arranged one after another on a cylinder row line of a cylinder block of the internal combustion engine; and a cooling condition of the cylinder bores is controlled by regulating a flow of cooling water in the water jacket by use of the spacer.
2. Description of the Related Art
Japanese Patent No. 4149322 has made publicly known a cooling structure for an internal combustion engine in which: six spacers for inhibiting the flow of cooling water are arranged inside a water jacket which surrounds peripheries of three cylinder bores arranged in a straight line; an upper support leg and a lower support leg respectively project upward and downward from a spacer main body part of each spacer; and the spacers are positioned in the water jacket in an up-and-down direction by use of those support legs.
Meanwhile, in the conventional cooling structure for an internal combustion engine, however, the six spacers are arranged at the farthest positions from a cylinder row line on the intake side and the exhaust side in the water jacket. For this reason, due to the support legs, each portion in which the corresponding spacer is arranged has a smaller cross-sectional area of the water jacket than two sides of the portion in which the spacer is arranged. This leads to a problem that: the flow of the cooling water is obstructed around the support legs; and the cooling performance is deteriorated.
The temperature of each cylinder bore tends to become higher particularly in the intake-side and exhaust-side positions with respect to the cylinder row line than in positions of the two end portions in the cylinder row line direction. When the flow of the cooling water is obstructed as a result of providing the support legs in the areas where the temperatures tend to become higher, the temperatures of the respective cylinder bores are likely to become nonuniform.